The invention relates to a process for determining the position of a positioning body relative to a reference body wherein the positioning body has a scale with marks of constant distances and the, reference body has a scanner onto which the marks of the scale are projected, and devices to implement the respective process.
Such methods serve, e.g., to acquire during the control of measurement and production machines the distances between longitudinally moveable objects such as measuring heads, gripping arms or assembling arms. In so doing, the accuracy with which these distances can be determined is a decisive factor for the machining accuracy of the automatic device.
A process, which enables high accuracy of measurement independently of an exact guide of the scanner, is already known from the DE-OS 39 09 856. At the same time three marks of a scale are evaluated by a scanner. With two marks the angle of projection formed between a projection center and these marks would still depend on how far the center of projection is above the marks and how far it is moved sideways. With three marks it is possible to exactly determine the center of the projection by way of another angle of projection formed between the center of projection, the third mark and one of the other two marks. For a combination of two angles there exists only one place where the center of projection can be located.
Furthermore, it is well-known from the book by G. Konecny and G. Lehmann: Photogrammetry, 4th edition, de Gruyter, Berlin, N.Y., 1984, pp. 48-55, to utilize a projective relationship to determine the coordinates and to consider a tilt angle between a projection area and a pre-image plane.